Consciousness can factually exist even though another being’s subjective experience is not directly observable. we can measure its behavioral and neural correlates and infer consciousness from them but we cannot directly observe the experience itself or conclusively prove its absence in another being. I don't think we'll ever get to a point where subjective experience in another is directly observable. But I don't think we need that to happen to prove consciousness factually exists.
Correlates to what exactly? To behavior or processes we assume subjective experience is present in?
That a thing is /red/ is directly observable (by people with good eyesight etc) but what the OP was ineptly driving at presumably holds of redness.